The present invention relates to the field of instrumented assemblies of the kind for control or operating wheels used, for example, to steer motor vehicles, handling vehicles or civil engineering works vehicles or any other type of vehicle or machine requiring a steering wheel.
In the conventional way, a control wheel is connected to a shaft, for example a steering column shaft, which, depending on the type of steering used, either directly turns the steering mechanism in the case of mechanical steering, actuates hydraulic pressure distributors in the case of hydraulic steering or, finally, in the case of electric steering, actuates the encoderring of a sensor delivering a signal to the electric control motor, various combinations of these types being possible.
In the case of purely electrical steering, which is increasingly commonly in use on handling vehicles such as fork lift trucks. A system detecting the rotation of the wheel, which may or may not be incorporated into the bearings, delivers, via a cable, a signal representative of the turning of the wheel to the device for steering the wheels of the vehicle. As the wheel is mounted on its support by one or more antifriction bearings and is not connected to mechanical torque-transmitting systems, the wheel can be turned with an extremely low resistive torque. Often added to this is a wheel-braking system intended to generate therein a resistive torque so as to encourage precision and driveability in the driving of the vehicle. A device of this type is described, for example, in document DE-A-195 10 717.
This device does, however, exhibit certain disadvantages among which we shall take note first of all of the relatively great axial bulk and the relatively high cost which are due to the presence of two antifriction bearings in the continuation of which is arranged a braking system employing a coil spring which presses a conical friction piece into a cup which also has a conical friction surface. The frictional torque developed by such a device is relatively low and the wear is high because of the small friction surfaces. Furthermore, the braking system alters the operating play in the bearings.
Document FR-A-2 782 970 discloses a control wheel mounted on an instrumented antifriction bearing and to which is added a braking system, the rotating part of which is supported by the rotating inner ring of the antifriction bearing and rubs against the end wall of a housing. However, in this type of device, the antifriction bearing is not mounted on a shaft and the diametral bulk of the bearing and of the device is great.
The invention proposes to overcome the disadvantages of the devices of the prior art.